- Geochemistry
Shaking out water's dusty origin
- Brent Grocholski
Basalt lavas at Cape Mercy, Baffin Island
PHOTO: GM PHOTO IMAGES/ALAMY
Where did Earth's water come from? Lavas erupting on Baffin Island, Canada, tap a part of Earth's mantle isolated from convective mixing. Hallis et al. studied hydrogen isotopes in the lavas that help to “fingerprint” the origin of water from what could be a primordial reservoir. The isotope ratios for the Baffin Island basalt lavas suggest a pre-solar origin of water in Earth, probably delivered by adsorption onto dust grains.
Science, this issue p. 795
- Genome Editing
Genome editing with a Cas9 scalpel
- Guy Riddihough
The Cas9 nuclease forms the heart of the CRISPR-Cas genome editing system. Cas9 binds small guide RNAs that direct it to its target sites, where the nuclease either cleaves or binds to genomic DNA. Knight et al. used single-molecule imaging to track Cas9 in living cells. Cas9 searches the genome for its target sites using rapid threedimensional diffusion. It spends very little time binding to off-target sites, which explains the high accuracy of the CRISPRCas9 editing machine.
Science, this issue p. 823
- Attosecond Dynamics
Electronic movement flashing into view
- Jake Yeston
Numerous chemical processes begin with ionization: the ejection of an electron from a molecule. What happens in the immediate aftermath of that event? Kraus et al. explored this question in iodoacetylene by detecting and analyzing the spectrum of emitted high harmonics (see the Perspective by Ueda). They traced the migration of the residual positively charged hole along the molecular axis on a time scale faster than a quadrillionth of a second. They thereby characterized the capacity of a laser field to steer the hole's motion in appropriately oriented molecules.
- Gamma-Ray Astronomy
LMC pulsar's bright gamma-ray flashes
- Keith T. Smith
The pulsar was found in the 30 Doradus region of the Large Magellanic Cloud
PHOTO: TRAPPIST/E. JEHIN/ESO
Pulsars are rapidly rotating neutron stars that are seen as pulsating sources of radio waves. Some, such as the Crab pulsar, also emit pulses of gamma rays. The Fermi LAT collaboration observed pulsed gamma rays from a pulsar outside our galaxy, the Milky Way. The pulsar, known as PSR J0540–6919, is located in the Large Magellanic Cloud (LMC). This is the most powerful gamma-ray pulsar yet known, with luminosity 20 times that of the Crab. The findings should help to explain how pulsars convert the energy stored in their rotation into detectable electromagnetic emission.
Science, this issue p. 801
- Mucosal Immunity
A gut bacterial containment system
- Kristen L. Mueller
Trillions of bacteria selectively inhabit our guts, but how do our bodies keep them contained? Spadoni et al. describe a “gut-vascular barrier” that prevents intestinal microbes from accessing the liver and the bloodstream in mice (see the Perspective by Bouziat and Jabri). Studies with human samples and in mice revealed that the cell biology of the gut-vascular barrier shares similarities with the blood-brain barrier of the central nervous system. Pathogenic bacteria such as Salmonella typhimurium could penetrate the gut-vascular barrier in mice, gaining access to the liver and bloodstream, in a manner dependent on the Salmonella pathogenicity island 2–type III secretion system.
- Human Evolution
Ancient African helps to explain the present
- Laura M. Zahn
Tracing the migrations of anatomically modern humans has been complicated by human movements both out of and into Africa, especially in relatively recent history. Gallego Llorente et al. sequenced an Ethiopian individual, “Mota,” who lived approximately 4500 years ago, predating one such wave of individuals into Africa from Eurasia. The genetic information from Mota suggests that present-day Sardinians were the likely source of the Eurasian backflow. Furthermore, 4 to 7% of most African genomes, including Yoruba and Mbuti Pygmies, originated from this Eurasian gene flow.
Science, this issue p. 820
- GPCR Signaling
Receptor methylation controls behavior
- John F. Foley
D2 dopamine receptors are targeted by antipsychotic agents to regulate behavior. Likhite et al. found putative arginine methylation motifs in some human G protein–coupled receptors (GPCRs), including the D2 dopamine receptor, and in homologs in the worm Caenorhabditis elegans. Methylation of the D2 dopamine receptor by the arginine methyltransferase PRMT5 enhanced D2 receptor signaling in cultured cells. C. elegans lacking prmt-5 had behavioral problems similar to those in worms deficient in the D2-like receptor DOP-3. Thus, methylation of GPCRs may be important for clinically relevant targets such as the D2 receptor.
Sci. Signal. 8, ra115 (2015).
- Neurotechnology
Tireless typing with the brain
- Megan Frisk
It's already a technological feat that the brain can be hooked up to a computer to allow paralyzed individuals to type. But these so-called brain-computer interface (BCI) technologies can be tiring and burdensome for users, requiring frequent breaks and recalibration while mentally typing short texts. Jarosiewicz et al. combined three calibration methods—retrospective target interference, velocity bias correction, and adaptive tracking of neural features—in the optimal configuration for seamless typing and stable neural control. The combination allowed four individuals with tetraplegia to compose longer texts at their own pace, with no need to pause for recalibration.
Sci. Transl. Med. 7, 313ra179 (2015).
- Climate Change
Double jeopardy
- Sacha Vignieri
In the best of worlds, exploited fish stocks are monitored so that harvest quotas protect the reproductive ability of the population. Climate change is likely to complicate this process substantially. Pershing et al. found that cod stocks declined continuously during intense warming in the North Atlantic. Fisheries quotas, even though they were responsibly set and followed by fishers, decreased the reproductive rate. Thus, managing fisheries in a warming world is going to be increasingly problematic.
Science, this issue p. 809
- Growth Control
Brain keeps body size and shape in check
- Beverly A. Purnell
Animal systems show amazing left-right symmetry—think of how our legs or arms, or the legs or wings of an insect, are matched in size and shape. Environmental insults and growth defects can challenge these developmental programs. In order to limit the resultant variation, juvenile organisms buffer variability through homeostatic mechanisms, so that the correct final size is attained. Vallejo et al. report that the Drosophila brain mediates such homeostatic control via an insulin-like peptide Dilp8 binding to the relaxin hormone receptor Lgr3. Lgr3 neurons distribute this information to other neuronal populations to adjust the hormones ecdysone, insulin, and juvenile hormone in a manner that stabilizes body and organ size.
Science, this issue p. 10.1126/science.aac6767
- Magnetic Resonance
Mechanically detected spin resonances
- Phil Szuromi
The interaction of spins in a sample with a magnetic field can generate forces that can be sensed with cantilever probes. Losby et al. measured the resonance signals at room temperature with a micromechanical torque magnetometer. The difference between two applied radio-frequency signals corresponded to the mechanical frequency of the resonator. This approach revealed the vortex core dynamics of the ferri-toferro–magnetic transition in a micrometer-sized yttrium-iron-garnet single-crystal disk.
Science, this issue p. 798
- Scattering Dynamics
Watching collisions in the slow lane
- Jake Yeston
Quantum mechanics aims to “micromanage” the details of collisions between atoms and molecules. However, it's hard to discern all the subtleties under high-energy conditions. Vogels et al. slowed down two intersecting beams of helium atoms and nitric oxide (NO) molecules to a relative crawl in order to characterize the collisions precisely. The data revealed short-lived resonances that matched theoretical predictions remarkably well—a striking feat on both sides, given the challenge of accurately modeling NO's unpaired electron. The study highlights chemists' increasingly sophisticated understanding of collision dynamics.
Science, this issue p. 787
- Extinction Events
The small will inherit the Earth…
- Sacha Vignieri
Understanding how communities and ecosystems recovered from the previous five global extinction events sheds light on how extinctions shape broad patterns of biodiversity. Sallan et al. looked across vertebrate species during and after the Devonian extinction (see the Perspective by Wagner). Small-bodied species, with rapid reproductive rates, dominated post-extinction communities, despite the presence of many successful large-bodied species before the extinction. This pattern mimics, to some degree, current patterns of extinction, suggesting that we might expect similar loss of large-bodied species if we continue along our current path.
- Mammalian Evolution
Moving mammoths
- Sacha Vignieri
Mammoths are a particularly charismatic example of our Pleistocene megafuana. Lister and Sher took a detailed look at mammoth fossils globally and suggest that the North American Columbian mammoth, thought to have arisen from a European species, probably evolved from a more advanced Asian species. Similar dispersal events of Asian mammoths led to later colonization events in Europe and North America.
Science, this issue p. 805
- Antiviral Immunity
Nlrp6 keeps gut infections in check
- Kristen L. Mueller
Most viruses infect only certain cells of the body. Enteric viruses, such as norovirus and rotavirus, specifically infect the gut. Wang et al. now show that the response to such viruses is tissue-specific, too. Antiviral immunity to enteric but not systemic viral infections in mice required Nlrp6, a member of the NOD-like receptor family of proteins that play important roles in host defense. Together with the RNA helicase protein Dhx15, Nlrp6 bound viral RNA and elicited downstream antiviral immune responses necessary for viral clearance. These included the production of type I and type III interferons and the expression of interferon-stimulated genes.
Science, this issue p. 826
- Small RNAs
MicroRNAs that control behavior
- Guy Riddihough
MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene activity. They repress expression through complementary base pairing interactions with target messenger RNAs. MiRNAs are involved in regulating many cell and developmental processes. Picao-Osorio et al find that miRNAs can also control behavior in the fruit fly Drosophila. A specific miRNA locus regulates the self-righting response in larva that ate tipped over onto their backs. The miRNA locus targets a gene required for the normal activity of two neurons involved in the self-righting response.
Science, this issue p. 815
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